More than 10 years have passed since the regulation of automotive exhaust gases was put into effect, and now exhaust gases are regulated based on improvements to the engine and the catalytic conversion. The majority of currently available catalysts for the purification of exhaust gases have a structure in which a gamma-alumina powder is supported, and which carriers a precious metal such as Pt on a ceramic honeycomb such as CORDIOLITE. This ceramic honeycomb has a relatively high resistance to the exhaust gas and a limited thermal resistance of the stainless steel mesh buffer inserted between the honeycomb and the jacket for preventing rupture of the honeycomb, and thus the honeycomb must be operated at a relatively low temperature.
Currently, metallic carriers made of stainless steel foils and capable of overcoming the above-mentioned drawback of the conventional catalyst carriers have been proposed and have attracted attention in the industries concerned. Generally, the metallic carriers are composed of a honeycomb formed by laminating or winding a flat metal foil (flat foil) and a corrugated metal foil (corrugated foil), and metallic jacket which houses the honeycomb. Of course, they must have a thermal resistance sufficient to withstand high temperature and high speed exhaust gases in a reaction, and a heat and fatigue resistance making them durable against severe heating and cooling conditions.
For a metallic carrier capable of withstanding the hot and high speed exhaust gases, effectively stainless steel foils having a superior oxidation resistance are used and increased a mutual joining area, but the metallic carrier of only this structure cannot withstand severe cooling and heating. Namely, in the metallic carrier mounted in the exhaust system of an automobile, the honeycomb is heated before the jacket during start up and acceleration. In the case of an engine system in which the engine brake is applied for deceleration and the fuel supply is stopped, the honeycomb is cooled before the outer cylinder, and thus a large difference in temperature between the jacket and honeycomb occurs together with the temperature distribution in the honeycomb. The temperature difference is different during acceleration than during deceleration, and generally, since the honeycomb is made of a material having a thermal expansion coefficient different to that of the material used for the jacket, a large thermal stress occurs in the vicinity of the outer circumference of the honeycomb. Accordingly, the honeycomb is ruptured at the portion thereof near the jacket, and thus the honeycomb is moved away to the downwind side of the exhaust gas flow by the back pressure thereof.
To overcome the drawbacks of the conventional metallic carriers in which all the foils are securely joined together, methods of mechanically fixing of the honeycomb are known from U.S. Pat. No. 4,186,172 and Japanese Examined Patent Publication (Kokoku) No. 60-27807, etc. Further, methods of a partial joining of the honeycomb are known from Japanese Unexamined Patent Publication (Kokai) Nos. 62-45345 and 61-199574. These publications do not definitely disclosed methods of joining the honeycomb and jacket to each other. As disclosed in, for example, Japanese Unexamined Patent Publication No. 61-199574, the flat and corrugated foils are joined together only at the opposite ends of the honeycomb body, and they are not joined in the intermediate portion between the honeycomb-body ends. In this structure, the joining between the honeycomb body and jacket is very unstable, and is unsatisfactory from the viewpoint of at least one of the strength of the joining of the honeycomb body to the jacket and the heat and fatigue resistance. Also Japanese Unexamined Utility Model Publication No. 62-160728 discloses a method of mechanically fixing the honeycomb body to the jacket. In this structure, however, which is separate from the jacket, the honeycomb body vibrates inside the jacket so that the catalyst supported thereby is likely to fall out, resulting in a reduced catalytic conversion of the exhaust gases.
Further, Japanese Unexamined Utility Model Publication No. 62-194436 discloses a metallic honeycomb carrier in which the honeycomb body is joined at the outer circumference thereof to the inner face of the jacket only at one cross section of the latter. Also, Japanese Unexamined Patent Publication Nos. 62-273050 and 62-273051 disclose structures in which only the ends of the foils are axially joined to the jacket but the flat and corrugated foils are not joined together, to suppress the thermal stress and thermal fatigue caused by the heat cycle, and further, Japanese Unexamined Patent Publication No. 62-83044 discloses a method of making a honeycomb structure which incurs only a minimum thermal stress by also waving the flat foil at long intervals and forming waves of short intervals in the corrugated foil to give an extra allowance for deformation in the cells of honeycomb body formed at the junctions. These conventional methods, however, cannot provide a structure in which the junctions between the flat and corrugated foils inside the honeycomb body can sufficiently withstand the hot and high speed exhaust gases.